Title: Modeling sorption and degradation of 17B-estradiol-17-sulfate in agricultural soils Authors
|Bai, Xuelian -|
|Casey, Francis -|
|Shrestha, Suman -|
|Desutter, Thomas -|
|Khan, Eakalak -|
|Oduor, Peter -|
Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: August 2, 2013
Publication Date: December 5, 2011
Citation: Bai, X., Casey, F.X.M., Hakk, H., Shrestha, S.L., Desutter, T.M., Khan, E., Oduor, P.G. 2011. Modeling sorption and degradation of 17B-estradiol-17-sulfate in agricultural soils. American Geophysical Union. American Geophysical Union Annual Meeting, December 5-9, 2011, San Francisco, CA. Interpretive Summary: 17B-Estradiol (E2) is a natural steroid hormone found in all vertebrates, and is a potent endocrine disrupting compound, particularly to aquatic life, operating through the estrogen receptor. Production animals excrete relatively large amounts of this hormone, and its transport into the environment is the subject of intense scientific inquiry. Laboratory studies suggest no E2 should reach surface or groundwater, but detections in these systems are frequent, and of a concentration to suggest that some endocrine disruption may occur to exposed wildlife populations. A possible means of environmental introduction may be as hormone conjugates, i.e. polar metabolites which can break down to the parent compound. We synthesized a radioactive version of a common E2 conjugate in swine, i.e. E2-17-sulfate (E2-17S), and measured its behavior in soil/water systems. About 3/4ths of the E2-17S sorbed to soil in 14 d, with nearly twice as much remained in aqueous solution when the soil organic content was low. Under sterile conditions, nearly twice as much E2-17S remained in aqueous solution when compared to the comparable high and low organic content natural soils. Already at 4 h the E2-17S remained began to degrade and form two polar metabolites. The aqueous composition of these polar metabolites increased in for the next 14 d, but no parent E2 was detected. This data indicated that E2-17S did not readily degrade to E2 in the experimental time frame selected, and at this time does not explain how E2 is transported to surface and groundwater. Qualitatively the same results were obtained for sterile soil, suggesting E2-17S is not a preferred substrate for microorganisms involved in environmental decomposition.
Technical Abstract: The natural steroid hormone, 17B-estradiol (E2), can be an endocrine disruptor at part-per trillion levels. Laboratory studies indicate a low potential for E2 persistence and mobility in the environment; however, field studies consistently indicate the presence of E2 and its primary metabolite, estrone, at levels sufficiently high to impact water quality. To facilitate urine excretion, animals may release E2 as a sulfated conjugate, which would have a higher aqueous solubility than the parent compound. We hypothesize that E2 conjugates contribute to the detection of free estrogens in the environment. The objective of this study was to determine the sorption, degradation, and mobility of a model conjugate, 17B-estradiol-17-sulfate (E2-17S), in agricultural soils. Radiolabeled E2-17S ([14C]E2-17S) was chemically synthesized in a three-step process, and then batch experiments were conducted in natural and sterile soils. Additionally, soil organic carbon (OC) was varied (1.29 and 0.26%) to investigate its effect on the fate of [14C]E2-17S. Liquid scintillation counting (LSC) was used in concert with high performance liquid chromatography (HPLC) to detect and quantitate parent compound and metabolites of E2-17S in the aqueous and bound phases. Residual soil was combusted to determine non-extractable levels of 14C. The E2-17S was relatively stable in the aqueous phase for natural and sterile soils. Mono- and di- hydroxyl E2-17S were detected as metabolites of E2-17S in the aqueous phase above both sterile and natural soil. Deconjugation to form E2 was not observed in aqueous phase; however, E2 and estrone were extracted from both natural and sterile soils. A conceptual model was developed to simulate and identify the fate and transport processes of E2-17S. Organic carbon was found to be an important factor affecting the sorption and degradation of E2-17S in soils.